Michael Cohen is emerging as a pivotal figure with knowledge of contacts between the Trump campaign and Russia, a new court filing Friday from special counsel Robert Mueller suggests.

The Mueller sentencing memo suggests that Trump’s former personal attorney provided answers on matters at the very heart of the investigation. Per the document, Cohen’s cooperation allowed the special counsel to conclude that the Trump Organization was enthusiastically seeking business opportunities in Russia—and direct contact with the Russian government—while Trump was running for president.

Referring to the Trump Organization’s plans to develop a Trump Tower Moscow, which lasted through June 2016, Mueller said that the matter was “material to the ongoing congressional and SCO investigations” and “occurred at a time of sustained efforts by the Russian government to interfere with the U.S. presidential election.”

Cohen contacted Russian President Vladimir Putin’s press secretary to try to get the project underway, and worked with Trump Organization associate and convicted felon Felix Sater to advance it.

Rather than just a project that was discussed and never seriously pursued, Cohen informed Mueller that the development “would have made it highly lucrative for [the Trump org] and himself.”

Buzzfeed reported in June that Ivanka Trump had connected Cohen with a Russian Olympic weightlifter named Dmitry Klokov. The story suggests that Klokov was offering to connect Trump with Putin in the fall of 2015, in part to “pave the way” for the Trump Tower Moscow project.

Per the memo, Cohen also spoke to Trump about connecting with Putin in person when he was in New York in 2015 for the UN General Assembly. Cohen was also contacted, in the lead-up to the 2016 election, by a Russian national claiming to be a “trusted person” in Russia’s government, who said he could offer “political synergy” to Trump’s campaign.

All of these remarkable developments shed new light on the extent of Trumpworld connections with Russia from 2015 onward, and put Cohen—then Trump’s top lieutenant and “pit bull”—at the center of that matrix.